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    Effect of inclination angle on the pull-out strength of bonded anchors installed in low-strength concrete
    (Elsevier, 2023) Cihan, M. Timur; Aydin, Zekeriya; Cinar, Kenan
    Bonded anchors are commonly used in the strengthening of reinforced concrete structures to ensure effective bonding between the existing and new concrete. In chemical-anchor applications, the anchor direction is typically perpendicular to the concrete surface. Most approaches adopted to design chemical anchors assume that the anchor direction is the same as the direction normal to the concrete surface. However, owing to certain requirements or application errors, the anchor direction may differ from the direction normal to the concrete surface. In this study, the effect of the inclination angle on the anchor strength was experimentally investigated. In addition to the inclination angle, the anchor embedment depth and concrete strength were also considered. As the concrete strength is generally lower than the design strength of reinforced concrete buildings that need to be strengthened, low-strength concrete was considered in our analysis. During our analysis, pull-out tests were conducted on 30 samples for five different angles (0 & DEG;, 10 & DEG;, 20 & DEG;, 30 & DEG;, and 40 & DEG;), three embedment depths (64, 96, and 128 mm), and two concrete grades. The results obtained from the experiments were analyzed and statistically evaluated. The analysis revealed that an inclination angle of up to 10 & DEG; did not have a significant effect on the pull-out strength, and the decrease in strength for angles up to 30 & DEG; could be compensated by an increase in the embedment depth. Moreover, some experiments showed that increasing the inclination angle can positively contribute to the energy absorption capacity of the joint.
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    Enhancement of laminate open-hole tensile strength by considering fiber waviness around holes
    (Elsevier Sci Ltd, 2024) Cinar, Kenan
    Bolted joints are widely used for joining laminated composites despite inducing stress concentrations and potential damage during drilling. This study explores an alternative approach using inserts embedded via vacuumassisted resin transfer molding (VARTM) to mitigate drilling-related issues. Mold-in cylindrical brass inserts were incorporated into the dry fabric and subsequently removed post-fabrication to assess their impact on open-hole tensile and bearing strength compared to drilled counterparts. Results show that non-drilled samples with various ply configurations exhibited significantly higher open-hole tensile loads-up to 54.8 %-compared to drilled samples, with similar bearing load values. A 3D progressive damage model incorporating fiber waviness around the hole was developed and validated by digital image correlation technique. Micro-CT images revealed improved fiber continuity around holes in non-drilled samples, supporting the observed strength improvements. Scanning electron microscope (SEM) images further elucidated failure mechanisms during bearing tests. The failure mechanism involves initial fiber kinking in the linear region (especially for drilled samples), followed by fiber crushing and fracture around the hole. Finally, fiber accumulation is disrupted by shearing. The non-drilling approach presents promising advancements in composite joint strength and durability.
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    Failure prediction of syntactic foam core L-shaped sandwich structures
    (Elsevier Sci Ltd, 2023) Cinar, Kenan; Inam, Okan
    L-shaped laminates with a syntactic foam core were manufactured to investigate the bending behavior of the sandwich structures including sharp corners. The bending behavior, initial, and progressive failure modes of the sandwich structure were analyzed by four-point bending tests and the finite element method. The cohesive zone model and Hashin's failure criteria were used for inter-laminar and intra-laminar failure of the laminates, respectively. The concrete damage plasticity model was proposed to model the foam material with considering different material properties in tension and compression. Mode-I and Mode-II fracture toughness of the foam was obtained to characterize the foam/laminate interface. Load-displacement curves predicted under bending simulation were quite well compliant with experimental results. The difference between numerical and experimental failure loads was 10.6 %, 1.2 %, and 1.9 % for the foam with facesheet stacking sequence of [0/90]2s, [0/ 90]3s, and [0/45/-45/90]2s, respectively. Predicted radial and hoop direction strain fields in the foam section were also compared to the measured one using a digital image correlation technique. Strain fields and failed regions and their mechanisms were captured well using the model. The initial failure mechanism was delamination at the interface between the foam and facesheet followed by foam tensile fracture.